1. Field of the Invention
The present invention relates to a semiconductor device using an oxide semiconductor, a method for manufacturing the semiconductor device, and an apparatus used for forming an oxide semiconductor film.
Note that in this specification, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all included in the category of semiconductor devices.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. Such transistors are applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). As materials of semiconductor thin films applicable to the transistors, silicon-based semiconductor materials have been widely used, but oxide semiconductors have been attracting attention as alternative materials.
For example, disclosure is made of a transistor having an active layer for which an oxide semiconductor that contains indium (In), gallium (Ga) and zinc (Zn) and has an electron carrier concentration less than 1018/cm3 is used, and a sputtering method is considered the most suitable as a method of forming a film of the oxide semiconductor (see Patent Document 1).
Moreover, there is a trend in an active matrix semiconductor device typified by a liquid crystal display device towards a larger screen, e.g., a 60-inch diagonal screen, and further, the development of an active matrix semiconductor device is aimed even at a screen size of a diagonal of 120 inches or more. In addition, a trend in resolution of a screen is toward higher definition, e.g., high-definition (HD) image quality (1366×768) or full high-definition (FHD) image quality (1920×1080), and prompt development of a so-called 4K Digital Cinema display device, which has a resolution of 3840×2048 or 4096×2180, is also pushed.
Such an increase in the size of a semiconductor device leads to an increase in the size of a glass substrate for production of a liquid crystal panel, for example, from a size of 300 mm×400 mm called the first generation to a size of 550 mm×650 mm of the third generation, 730 mm×920 mm of the fourth generation, 1000 mm×1200 mm of the fifth generation, 1450 mm×1850 mm of the sixth generation, 1870 mm×2200 mm of the seventh generation, 2000 mm×2400 mm of the eighth generation, 2400 mm×2800 mm of the ninth generation, or 2880 mm×3080 mm of the tenth generation. The size of a glass substrate is expected to be further increased to the size of the eleventh generation or the twelfth generation in the future.